Rear indicator fails after 35 mins driving

[Prof Yaffle]

Rather weird this one. After 35-40 mins driving the nearside rear indicator stops working. Outside temp or lights on or off or how much usage doesn't seem to make any difference. It still stops working after 35 mins. If I stop for a coffee....it starts to work again. Any ideas?
Stuart

 

[DPG]

Rather weird this one. After 35-40 mins driving the nearside rear indicator stops working. Outside temp or lights on or off or how much usage doesn't seem to make any difference. It still stops working after 35 mins. If I stop for a coffee....it starts to work again. Any ideas?
Stuart

First things first - check the contacts on the holder and the bulb. Apply a bit of contact cleaner as well.